Interpretive Summary: Carbon black is a petroleum derived product that has been used for decades as filler to strengthen rubber composites. It has excellent reinforcement properties but with both the cost and demand of petroleum rising, it is wise to look for renewable replacement materials. Biochar is the solid charcoal that comes from heating plant or animal materials (or any other carbon-containing biomass) in the absence of oxygen. Biochar is not as pure as carbon black, but may still be a useful substitute material as rubber composite filler. In this work, a low-ash (higher carbon content) biochar was tested both by itself and blended with carbon black at different concentrations to determine its reinforcement properties compared to a carbon black control. The results showed that although carbon black reinforced the rubber more effectively than biochar at higher concentrations, 25/75 and 50/50 biochar/carbon black blended composites at 10% total filler concentration had superior material properties compared to the carbon black-filled control. This means that for softer, more flexible rubber composites, biochar may be used as a partial replacement for carbon black and still improve the mechanical properties. This will reduce petroleum dependence and possibly cost, depending on current petroleum prices.

Technical Abstract:
A biochar made from woody waste feedstock with low ash content was blended with carbon black as filler for styrene-butadiene rubber. At 10% total filler concentration (w/w), composites made from 25 or 50% biochar showed improved tensile strength, elongation, and toughness compared to similar composites filled with carbon black. This demonstrates the potential to use renewable biochar as a partial substitute for carbon black in flexible, low-filler rubber composite applications.